Conventionally, ultrasound diagnosis apparatuses have often been used for performing a test on a tissue in a subject's body and providing Radio Frequency Ablation (RFA) treatments where a puncture process is performed while using a puncture needle, because ultrasound diagnosis apparatuses are capable of displaying an ultrasound image captured immediately underneath an ultrasound probe in a real-time manner. Depending on where the lesion is positioned and the angle at which a puncture needle is inserted, it can be difficult to see the puncture needle in some situations. In those situations, the puncture process is performed while checking on how the tissue moves when, for example, the puncture needle is moved around.
To cope with those situations, a technique is known these days by which, to improve the visibility of a puncture needle during a puncture process, an ultrasound beam is radiated perpendicularly to the puncture needle by performing an oblique scanning process, so as to generate an ultrasound image (a needle image) in which the puncture needle is rendered with a high level of brightness. Further, another technique is also known by which, without performing the oblique scanning process, a regular ultrasound scanning process is performed so as to generate, in addition to a needle image, an ultrasound image (a subject-body image) in which a tissue in the subject's body is rendered and so as to generate and display a synthesized image obtained by synthesizing together the needle image and the subject-body image. According to this technique, when the synthesized image is generated, one or more of the following processes are performed: a process to add together the needle image and the subject-body image; a process to superimpose the images with one another by averaging the pixel values for each of the pixels; and a process to hold the maximum value of brightness levels for each of the pixels (a maximum brightness value holding process or a Max-Hold process).
It should be noted, however, that the tissue in the subject's body rendered in the ultrasound image generated by performing the oblique scanning process has lower image quality than in an image obtained by performing a non-oblique scanning process, due to a side-lobe effect or the like. For this reason, although the visibility of the puncture needle in the synthesized image is improved to some extent, the diagnosability using the synthesized image is lower because it is not possible to perform a substantive observation on a lesion in the tissue in an optimal manner. In other words, a phenomenon occurs where, although the puncture needle is easier to see because the ultrasound beam is perpendicularly applied to the puncture needle, information about the tissue in the subject's body becomes degraded due to occurrence of, for example, a grating side-lobe caused by problems related to the shape of the beam or the like.